1. Field of the Invention
The present invention relates to a multi-window display device, which is also an EL display device, a liquid crystal display device, or other display devices and in which plural screens also called multi windows are displayed on a display screen, and relates to a method of driving such a display device.
2. Description of the Related Art
In recent years, there have been conducted researches on a multi-window display device in which two or more images (including a static image and a dynamic image) are simultaneously displayed on a display screen. The multi-window display device is a very convenient display device because a screen for explanation of operation and a screen for performing the operation are displayed at one time or because a navigation screen and a screen for displaying a rear portion of an automobile are displayed at one time in a car navigation system.
FIG. 11 shows a conventional multi-window display device. In the multi-window display device, since plural screens (for example, two screens) are simultaneously displayed on a display screen, a first video signal and a second video signal corresponding to two pieces of image information are inputted, and signal processing is performed in an IC (integrated circuit) 11. Conducted in the IC 11 is the signal processing for synthesizing the two pieces of image information (each including information on the relative position and the size) for the two screens. The above-described video signal synthesized in the IC 11 is once held in a memory 12, and then is inputted to a signal line driver circuit 13.
Then, a scanning line driver circuit 14 sequentially selects pixels in a pixel portion 15, and a first screen 16 and a second screen 17 are displayed in accordance with the video signals supplied from the signal line driver circuit 13.
That is, from the viewpoint of the display screen, the screens are displayed simply in accordance with the input video signals irrespective of whether the multi-window screens are displayed or not.
An example of the above-described operation method is described in JP 05-242232 A, in which a signal from a PC display control means and a signal from the outside are synthesized by a display synthesizing means to thereby be input to a display means.
Further, also described in JP 05-242232 A is a method of arbitrary displaying the relative position and the size of each screen, in which a display reading control means and also a display position/size control means vary an increasing rate of a row address in reading, and thin down a row read out from a display memory to thereby control the size in a vertical direction.
In the above-described displaying method, prior to inputting to the display, the following is merely carried out: signal processing is conducted to the video signal itself; the processed video signal is inputted to the display; and then, display is performed. Therefore, a circuit for conducting signal processing, for example, an integrated circuit becomes complicated in order to store in a memory video signals corresponding to plural screens.
Further, even the information on the position and size of each of the first screen and the second screen is stored in the memory. As a result, a load is further placed on the integrated circuit.